Prodrugs are modified form of drugs, which on activation form drugs. Recently some prodrugs of PBDs have been reported which do not get activated by the enzyme β-galactosidase (Marina J. Sagnou, Philip W. Howard, Stephen J. Gregson, Ebun Eno-Amooquaye, Philip J. Burke, David E. Thurston, Bioorg Med Chem. Lett. 2000, 10, 2083-2086; Jane M. Berry, Philip W. Howard, Lloyd R. Kelland, David E. Thurston, Bioorg Med Chem. Lett. 2002, 12, 1413-1416; Luke A. Masterson, Victoria J. Spanswick, John A. Hartley, Richard H. Begent, Philip W. Howard, David E. Thurston, Bioorg. Med. Chem. Lett. 2006, 16, 252-256).
Pyrrolo[2,1-c][1,4]benzodiazepine antitumour antibiotics are commonly known as anthramycin class of compounds. In the last few years, a growing interest has been shown in the development of new pyrrolo[2,1-c][1,4]benzodiazepines (PBDs). These PBDs are a family of sequence selective DNA-binding antitumour antibiotics that bind exclusively to the exocyclic N2-guanine in the minor groove of DNA via an acid-labile animal bond to the electrophilic imine at the N10-C11 position. (Kunimoto, S.; Masuda, T.; Kanbayashi, N.; Hamada, M.; Naganawa, H.; Miyamoto, M.; Takeuchi, T.; Unezawa, H. J. Antibiot., 1980, 33, 665.; Kohn, K. W.; Speous, C. L. J. Mol. Biol., 1970, 51, 551.; Hurley, L. H. Gairpla, C.; Zmijewski, M. Biochem. Biophys. Acta., 1977, 475, 521.; Kaplan, D. J.; Hurley, L. H. Biochemistry, 1981, 20, 7572.; Ahmed Kamal, G. Ramesh, N. Laxman, P. Ramulu, O. Srinivas, K. Neelima, Anand K. Kondapi, V. B. Sreenu, H. A. Nagarajaram. J. Med. Chem. 2002, 45, 4679-4688).
All biologically active PBDs possess the (S) configuration at the chiral C11a position, which provides the molecule with a right-handed twist, which allows them to follow the curvature of the minor groove of B-form double-stranded DNA spanning three base pairs. The PBDs are of considerable current interest due to their ability to recognize and subsequently form covalent bonds to specific base sequences of double-stranded DNA. Naturally occurring pyrrolo[2,1-c][1,4]benzodiazepines belong to a group of antitumour antibiotics derived from Streptomyces species with family members including anthramycin, tomaymycin, sibiromycin, chicamycin, neothramycins A and B, and DC-81.

However, the clinical efficacy for these antibiotics is hindered by several limitations, such as poor water solubility and cardiotoxicity and development of drug resistance, lack of tumour selectivity, metabolic inactivation. Therefore it is of considerable interest to design and prepare glycoside prodrugs of PBDs that could be activated by the enzyme β-galactosidase. This enzyme is found in some tissues like liver specifically or it can be delivered as an enzyme-antibody conjugate to the malignant cells. It is expected that these prodrugs get activated by the enzyme to the active moiety, and then interact with DNA.